1. Field of the Invention
The present invention relates to a laser beam printer (LBP), and in particular, to a method of controlling provision of a transfer voltage based on the specific resistance of paper in n laser beam printer (LBP).
2. Description of the Related Art
In general, a laser beam printer (LBP) exemplary of contemporary practice in the art includes a paper cassette and an image forming device such as a developer and a fixer for fixing a toner image onto a paper sheet, to print on the paper.
In a general laser beam printer (LBP) exemplary of contemporary practice in the art, plural sheets of paper loaded on a paper cassette are fed sheet by sheet by a pickup roller. Then, the paper reaches a pair of feed rollers with its leading end aligned, and a toner image is fixed onto the paper with high temperature and high pressure while the paper passes through a developer and a fixer. The image-formed paper comes out to a discharge plate through a discharge roller.
The above described laser beam printer (LBP) exemplary of contemporary practice in the art typically uses a conductive transfer roller, measures the specific resistance of the transfer roller varied with an environment, and applies a transfer voltage based on the transfer roller resistance. In fact, image quality is greatly affected by a variation in the specific resistance of paper, which is in turn influenced by the thickness, humidity, and quality of the paper. However, despite the great influence on image quality, the paper specific resistance is unduly neglected in the process of setting a transfer voltage in the laser beam printer (LBP) exemplary of contemporary practice in the art which gives consideration only to the resistance between the conductive transfer roller and a photosensitive drum.
U.S. Pat. No. 4,511,240 to Suzuki et al., entitled ELECTROSTATIC RECORDING APPARATUS, discloses an electrostatic recording apparatus having a sensor for detecting a surface potential of a photosensitive member on which an electrostatic latent image is formed and a controller for controlling a developing bias voltage in accordance with the detected surface potential. The developing bias voltage includes an AC component and a DC component which are selectively used in accordance with a latent image potential. It is disclosed that the frequency of the AC developing bias and the magnitude of the DC developing bias are variable so that an optimum quality of image is reproduced.
U.S. Pat. No. 5,099,287 to Sato, entitled TRANSFERRING VOLTAGE CONTROL SECTION, discloses an electrophotographic printing apparatus which includes a paper supplying mechanism for supplying recording paper, and a transferring section for charging the recording paper supplied from the paper supplying mechanism by means of a transferring voltage and for transferring development material adhered to the surface of a charging body of the apparatus to the charged recording paper. It is disclosed that the electrophotographic printing device further includes a transferring voltage control section for controlling the transferring voltage level according to the type of the recording paper.
U.S. Pat. No. 5,155,501 to Fujita et al., entitled ELECTROPHOTOGRAPHIC APPARATUS WITH FREQUENCY AND DUTY RATIO CONTROL, discloses an electrophotographic apparatus wherein a photosensitive body charged by a charger is exposed to light emitted from an exposer, for the formation of an electrostatic latent image, and wherein the electrostatic latent image is developed by a developer and the image developed by the developer is transferred on a paper sheet by a transfer charger. It is also disclosed that the transfer charger of the apparatus is made up of a converter transformer, a switching circuit for controlling the excitation of the converter transformer, and an error detector, arranged in association with the converter transformer, for detecting an error voltage corresponding to a transfer voltage. The apparatus is disclosed to include a separately (or externally) excited converter which outputs the transfer voltage from the secondary winding of the converter transformer, an input section from which one of the print density levels that are predetermined stepwise is designated, and a control section for controlling the frequency and duty ratio of a transfer signal used for causing the switching circuit to perform a switching action, in accordance with the print density level designated from the input section and the error voltage information supplied from the error detector.
U.S. Pat. No. 5,241,343 to Nishio, entitled CONDUCTIVE FOAM RUBBER ROLLER USED IN IMAGE FORMATION APPARATUS SUCH AS ELECTROPHOTOGRAPHIC APPARATUS, discloses an image formation apparatus such as an electrophotographic recording apparatus which uses a conductive foam rubber roller as a charging roller, developing roller, toner-removing roller, or transfer roller, and comprises a tubular roller element made of a conductive foam rubber material and having a central bore defined by a solid skin layer having an electric resistivity considerably higher than that of a foam structure of the rubber element, and a conductive shaft on which the roller element is mounted and fixed. It is disclosed that end sections of the skin layer are removed from the roller element such that the foam structure thereof is in direct contact with the shaft at end sections of the bore thereof. Alternatively, a conductive disc-like member having a central opening formed therein is inserted onto the shaft to be abutted against an end face of the roller element, whereby sufficient electric contact can be established between the roller element and the shaft.
U.S. Pat. No. 5,486,903 to Kanno et al., entitled IMAGE FORMING APPARATUS WITH PAPER THICKNESS DETECTOR, discloses a detection device for detecting the thickness of a recording material by using an air capacitor, and an image forming device for forming an image on the recording material on the basis of the output from the detection device.
U.S. Pat. No. 5,809,367 to Yoo et al., entitled METHOD OF AUTOMATICALLY CONTROLLING TRANSFER VOLTAGE AND FUSING TEMPERATURE IN AN ELECTROPHOTOGRAPHIC PRINTING APPARATUS, discloses a method of automatically controlling an electrophotographic printing apparatus' transfer voltage and fusing temperature according to the type of paper by an automatic mode change during manual paper feeding which includes the steps of following a manual feed option being selected, automatically converting the apparatus's normal paper mode into a paper selection mode in response to the manual paper feeding; and when a keyboard input is made indicating a change in the type of paper, setting the transferring voltage and fusing temperature according to the keyboard input and printing images corresponding to image data from a host computer system on the paper.
U.S. Pat. No. 5,848,321 to Roh et al., entitled METHOD FOR AUTOMATICALLY CONTROLLING TRANSFER VOLTAGE IN PRINTER USING ELECTROPHOTOGRAPHY SYSTEM, discloses an electrophotography machine that consistently produces images of optimum image density regardless of whether an ordinary sheet of paper or a transparency is used as the recording medium. A photosensor activated in response to the recording media passing a first sensor is disclosed to be positioned on the paper conveyance path and detects whether or not the recording media being processed is an ordinary sheet of paper or a transparency. It is further disclosed that a controller automatically applies the appropriate transfer voltage depending on whether or not the sheet of recording media is a sheet of paper or a transparency.
U.S. Pat. No. 5,887,220 to Nagaoka, entitled ELECTROPHOTOGRAPHIC PRINTER SENSING AMBIENT CONDITIONS WITHOUT SENSORS, discloses when an electrophotographic printer is manufactured, the initial electrical resistance of its transfer roller is measured and a corresponding value is stored in a memory device in the printer during operation, the printer's control program estimates the resistance of the transfer roller from the stored value, taking aging into account, then measures the actual resistance of the transfer roller, and infers ambient conditions from the difference between the estimated and actual resistance values. It is also disclosed that the electrophotographic printer is controlled according to the inferred ambient conditions.